Ž .
peroxide on day 22 after the end of the trial day 21 . The sample size for parasite enumeration was 20 fish per pen.
2.5. Data handling Ž
Parasite counts were summarised as chalimus copepodites, chalimus stages I, II, III .
Ž .
Ž and IV , motile lice pre-adult and adult stages and total lice chalimus and motile
. stages combined and the arithmetic means calculated. Parasite count data were sub-
jected to F-tests for homogeneity of variances and a correlation test to examine the normality of distribution. Lice numbers were analysed using the non-parametric STP test
Ž .
Sokhal and Rohlf, 1981 . In the two replicated trials, the data were analysed separately for each replicate pen.
The percentage reduction in mean total sea lice, over the trial period was calculated as follows:
Mean of control or treated replicates at day y1 Reduction s 100 y 100 =
.
ž
Mean of control or treated replicates at day 21 The efficacy or percentage reduction in mean total sea lice, relative to the control
groups, was calculated as follows: Mean of treated replicates
Efficacy s 100 y 100 = .
ž
Mean of the control replicates Owing to the high standard deviation of fish weights and the small sample size,
statistical analysis of fish weights was not appropriate in these trials. Specific growth Ž
. rates SGR were calculated as follows:
log e W y log e W
t
SGR s t
where W is the mean weight at day 21 and W is the mean weight at day y1 or y2.
t
3. Results
3.1. Feed consumption and fish weights In each trial, good feed consumption was observed in all treated and control pens
during and after the medication period. In the first trial, the increase in mean fish weight Ž
. Ž
. over the trial period was 5.2 g SGR 0.01 in the control group and 91.0 g SGR 0.8
Ž in the treated group. In the second trial, mean weights increased by 3.8 and 35.5 g SGR
. 0.03 and 0.3 in the control groups I and II, while treated pens I and II increased by
Ž .
92.7 and 133.4 g SGR 0.7 and 1.0 . In the third trial, owing to high fish weights and hence a high standard deviation, the sample size used was too small to provide
conclusive results on fish weights. No adverse effects or fish mortality were attributed to treatment with emamectin benzoate in any of the trials.
3.2. First trial 13.0–15.58C 3.2.1. First trial: efficacy against L. salmonis
The efficacy and mean numbers of L. salmonis per fish are shown in Table 1. Prior to the start of treatment, mean numbers of L. salmonis were similar in the two trial
pens. L. salmonis numbers increased in the control group by 52 over the trial period. In
the treated group, there was no corresponding increase and, from day y2 to 21, numbers decreased by 86. At day 21, treated fish had fewer motile and chalimus
stages than control fish. At the start of the trial, none of the fish examined was free of L. salmonis. At day 21, the number of L. salmonis on control fish ranged from 4 to 33,
while the range on treated fish was 0–11 and 43 of treated fish sampled had no chalimus or motile stages present.
3.2.2. First trial: efficacy against C. elongatus The results for C. elongatus are shown in Table 2. Prior to the start of treatment, the
mean numbers of C. elongatus were similar in the two trial pens. From day y2 to 21, the mean number of C. elongatus declined on control fish by only 36. Over the same
period, numbers fell on treated fish by 98. At the start of the trial, none of the fish sampled was free of C. elongatus. At day 21, 10 of treated fish had no motile C.
elongatus and 67 had no chalimus present whereas none of the control fish was free of chalimus or motile stages. Numbers of motile C. elongatus fell between days 7 and 14,
Table 1 First trial: Efficacy of emamectin benzoate against natural infestations of L. salmonis on Atlantic salmon. Fish
Ž .
received medicated feed at the rate of 0.5 biomass per day for 7 consecutive days days 0–6 . Sample size N s 30 fish per pen. Sea temperatures 13.0–15.58C
Time Nominal dose
Mean total lice Mean chalimus
Mean motiles Percent efficacy
y1
Ž .
Ž .
Ž .
Ž .
Ž .
mg kg S.D.
S.D. S.D.
total lice Ž
. Ž
. Ž
. Day y2
9.1 4.9 4.4 3.2
4.7 3.2 –
Ž .
pre-treatment Ž
. Ž
. Ž
. 50
10.0 5.3 5.2 4.8
4.8 2.6 Ž
. Ž
. Ž
. Day 7
17.0 6.0 5.8 2.7
11.3 5.0 45
Ž .
Ž .
Ž .
50 9.4 5.9
4.7 3.4 4.8 3.1
Ž .
Ž .
Ž .
Day 14 12.8 6.3
1.1 1.1 11.8 6.0
80 Ž
. Ž
. Ž
. 50
2.5 2.3 0.5 0.9
1.9 2.1 Ž
. Ž
. Ž
. Day 21
13.8 8.3 1.2 1.3
12.6 7.9 91
a
Ž .
Ž .
Ž .
50 1.4
2.3 0.2 0.5
1.2 2.0
a
Includes one fish with 11 lice.
Table 2 First trial: Efficacy of emamectin benzoate against natural infestations of C. elongatus on Atlantic salmon.
Ž .
Fish received medicated feed at the rate of 0.5 biomass per day for 7 consecutive days days 0–6 . Sample size N s 30 fish per pen. Sea temperatures 13.0–15.58C
Time Nominal dose Mean total lice Mean chalimus Mean motiles Percent efficacy
y1
Ž .
Ž .
Ž .
Ž .
Ž .
mg kg S.D.
S.D. S.D.
total lice Ž
. Ž
. Ž
. Ž
. Day y2 pre-treatment
41.9 8.3 26.2 8.8
15.6 5.5 –
Ž .
Ž .
Ž .
50 41.3 12.0
20.7 5.9 20.6 8.8
Ž .
Ž .
Ž .
Day 7 39.3 10.6
21.3 6.5 17.9 6.1
58 Ž
. Ž
. Ž
. 50
16.6 6.1 5.8 2.8
10.9 4.5 Ž
. Ž
. Ž
. Day 14
24.5 9.3 12.3 7.5
12.2 5.1 89
Ž .
Ž .
Ž .
50 2.6 3.2
1.0 2.3 1.5 1.3
Ž .
Ž .
Ž .
Day 21 26.8 13.4
14.9 9.4 11.9 6.4
84 Ž
. Ž
. Ž
. 50
4.3 5.2 0.5 0.9
3.8 4.8
following Aquagard
w
treatment of the commercial pens but numbers of chalimus had fallen between days 0 and 7, thus a decline in motile numbers was expected.
At day 14, 23 of fish in the control group had lesions caused by L. salmonis and C. elongatus while none of the treated fish examined were affected by sea lice damage.
Table 3 Second trial: Efficacy of emamectin benzoate against natural infestations of L. salmonis on Atlantic salmon.
Ž .
Fish received medicated feed at the rate of 0.5 biomass per day for 7 consecutive days days 0–6 . Sample size N s 20 fish per pen. Sea temperatures 13.8–14.28C
Time Nominal dose Mean total lice Mean chalimus Mean motiles Percent efficacy
y1
Ž .
Ž .
Ž .
Ž .
mg kg S.D.
S.D. S.D.
relative to controls Ž
. Ž
. replicate
total lice Ž
. Ž .
Ž .
Ž .
Ž .
Day y2 pre-treatment 0 I
18.7 8.1 3.6 3.3
15.1 6.7 –
Ž . Ž
. Ž
. Ž
. 0 II
20.4 8.5 6.5 4.1
13.9 5.7 Ž .
Ž .
Ž .
Ž .
50 I 16.2 6.4
2.9 2.6 13.3 5.3
Ž . Ž
. Ž
. Ž
. 50 II
26.9 9.4 8.3 4.2
18.6 8.5 Ž .
Ž .
Ž .
Ž .
Day 7 0 I
30.3 7.7 11.5 5.8
18.8 4.8 63.3
Ž . Ž
. Ž
. Ž
. 0 II
38.3 14.6 19.6 10.3
18.9 7.1 Ž .
Ž .
Ž .
Ž .
50 I 10.3 5.4
2.4 1.8 7.9 4.5
Ž . Ž
. Ž
. Ž
. 50 II
14.9 5.9 7.5 4.4
7.5 3.3 Ž .
Ž .
Ž .
Ž .
Day 14 0 I
31.7 8.2 15.6 5.2
16.2 5.2 93.4
Ž . Ž
. Ž
. Ž
. 0 II
65.9 34.0 41.2 23.1
24.8 12.6 Ž .
Ž .
Ž .
Ž .
50 I 2.3 1.7
0.8 1.0 1.5 1.5
Ž . Ž
. Ž
. Ž
. 50 II
4.0 4.6 3.3 3.8
0.8 1.1 Ž .
Ž .
Ž .
Ž .
Day 21 0 I
58.5 18.9 26.7 10.8
31.8 10.7 99.3
Ž . Ž
. Ž
. Ž
. 0 II
92.1 39.7 41.5 26.7
31.8 20.8 Ž .
Ž .
Ž .
50 I 0.3 0.7
0.3 0.7 Ž .
Ž .
Ž .
Ž .
50 II 0.8 1.2
0.6 0.9 0.2 0.4
3.3. Second trial 13.8–14.28C 3.3.1. Second trial: efficacy against L. salmonis
The efficacy and mean numbers of L. salmonis per fish are shown in Table 3. Prior Ž
to the start of treatment, one pen intended for treatment had significantly P - 0.05 and .
P - 0.01 more L. salmonis than one control pen and the other treated pen. Over the trial period, L. salmonis numbers increased by 284 in the two control
groups. In the two treated groups there was no corresponding increase and, from days y2 to 21, numbers declined by 97 on treated fish. At days 7, 14 and 21 both treated
Ž .
pens had significantly P - 0.01 fewer L. salmonis than fish in the two control pens. Ž
. Although control group I had significantly P - 0.05 fewer lice than control group II at
day 21, both groups still had large numbers of lice present and there were no significant Ž
. P 0.05 differences between the two treated replicates at days 14 and 21. At day 21,
individual control fish had 26–190 L. salmonis present but the highest number of L. salmonis found on any treated fish was 5 and 67.5 of treated fish had no L. salmonis
present. At day 14, the two treated pens had means of only 0.6 and 2.6 copepodites per fish
and there was less than 0.8 chalimus present. In contrast, all control fish had large numbers of copepodites and chalimus stages I, II, III and IV present. At day 21, the two
control groups had high numbers of chalimus present but there were no surviving
Table 4 Second trial: Efficacy of emamectin benzoate against natural infestations of C. elongatus on Atlantic salmon.
Ž .
Fish received medicated feed at the rate of 0.5 biomass per day for 7 consecutive days days 0–6 . Sample size N s 20 fish per pen. Sea temperatures 13.8–14.28C
Time Nominal dose Mean total lice Mean chalimus Mean motiles Percent efficacy
y1
Ž .
Ž .
Ž .
Ž .
mg kg S.D.
S.D. S.D.
relative to controls Ž
. Ž
. replicate
total lice Ž
. Ž .
Ž .
Ž .
Ž .
Day y2 pre-treatment 0 I
25.3 10.4 13.2 6.1
12.2 6.6 –
Ž . Ž
. Ž
. Ž
. 0 II
29.2 7.1 15.8 6.3
13.4 4.4 Ž .
Ž .
Ž .
Ž .
50 I 26.3 10.4
13.6 5.6 12.7 5.9
Ž . Ž
. Ž
. Ž
. 50 II
39.1 7.6 22.5 7.7
16.6 5.5 Ž .
Ž .
Ž .
Ž .
Day 7 0 I
20.3 8.4 6.5 3.4
13.8 7.3 45.6
Ž . Ž
. Ž
. Ž
. 0 II
20.4 7.6 9.2 5.0
11.4 4.6 Ž .
Ž .
Ž .
Ž .
50 I 8.2 8.2
3.2 2.3 5.1 2.7
Ž . Ž
. Ž
. Ž
. 50 II
14.0 7.1 6.3 3.3
7.7 4.7 Ž .
Ž .
Ž .
Ž .
Day 14 0 I
11.0 3.8 4.8 2.8
6.2 2.8 79.9
Ž . Ž
. Ž
. Ž
. 0 II
16.9 10.9 9.9 7.9
7.0 3.8 Ž .
Ž .
Ž .
Ž .
50 I 1.9 2.1
0.6 0.8 1.3 1.6
Ž . Ž
. Ž
. Ž
. 50 II
3.7 2.9 3.3 2.4
0.4 0.8 Ž .
Ž .
Ž .
Ž .
Day 21 0 I
10.5 4.2 4.6 2.3
5.9 2.9 81.9
Ž . Ž
. Ž
. Ž
. 0 II
12.6 4.4 6.2 3.2
6.4 3.1 Ž .
Ž .
Ž .
Ž .
50 I 1.3 1.2
0.6 0.6 0.7 0.8
Ž . Ž
. Ž
. Ž
. 50 II
2.9 2.3 2.5 2.2
0.5 0.8
chalimus on fish in one treated pen and means of only 0.5 copepodites and 0.1 chalimus IV in the other treated pen.
3.3.2. Second trial: efficacy against C. elongatus At the start of the trial, there was a high mean number of C. elongatus in each pen
Ž .
Ž .
Table 4 . Treated pen II had significantly P - 0.01 more C. elongatus than the other three pens prior to the start of treatment.
Over the trial period, the mean number of C. elongatus declined by 57 on control fish and by 94 on fish in the two treated groups. Numbers in both treated pens were
Ž .
significantly P - 0.01 lower than on control fish at days 14 and 21. At day 21, 84 and 100 of the immature stages remaining on treated fish were copepodites, whereas
in the control groups, only 37 and 34 of the immature stages were copepodites. Prevalence of C. elongatus declined from 100 to 35 of treated fish with motile
stages and 67.5 with chalimus, whereas none of the control fish sampled were free of chalimus or motile stages.
At day y2, the majority of fish sampled in each trial pen had skin lesions caused by sea lice. At day 21, the prevalence of lice damage on treated fish had fallen to only
12.5, while 77.5 of control fish were still affected.
Table 5 Third trial: Efficacy of emamectin benzoate against natural infestations of sea lice, L. salmonis, on Atlantic
salmon, S. salar. Fish received medicated feed at the rate of 0.5 biomass per day for 7 consecutive days Ž
. days 0–6 . The mean number of sea lice was determined on days y2, 7, 14 and 21. Sample size N s 20 fish
per pen. Sea temperatures 7.2–8.58C Time
Nominal dose Mean total lice Mean chalimus Mean motiles Percent efficacy
y1
Ž .
Ž .
Ž .
Ž .
mg kg S.D.
S.D. S.D.
relative to controls Ž
. Ž
. replicate
total lice Ž
. Ž .
Ž .
Ž .
Ž .
Day y1 pre-treatment 0 I
24.6 16.3 11.4 11.1
13.3 7.1 –
Ž . Ž
. Ž
. Ž
. 0 II
25.7 13.4 11.5 6.9
14.1 8.2 Ž .
Ž .
Ž .
Ž .
50 I 17.9 7.4
9.7 5.1 8.2 3.8
Ž . Ž
. Ž
. Ž
. 50 II
24.9 9.5 7.7 4.7
17.3 6.8 Ž .
Ž .
Ž .
Ž .
Day 7 0 I
23.3 14.7 10.5 9.4
12.8 7.0 25.4
Ž . Ž
. Ž
. Ž
. 0 II
27.8 11.1 10.3 6.5
17.6 7.5 Ž .
Ž .
Ž .
Ž .
50 I 13.5 5.9
7.1 4.3 6.4 2.8
Ž . Ž
. Ž
. Ž
. 50 II
24.7 12.1 7.1 5.4
17.6 8.9 Ž .
Ž .
Ž .
Ž .
Day 14 0 I
39.5 21.6 17.3 11.1
22.2 12.3 74.2
Ž . Ž
. Ž
. Ž
. 0 II
38.1 14.3 18.0 9.9
20.1 8.1 Ž .
Ž .
Ž .
Ž .
50 I 6.7 3.0
4.6 2.1 2.2 1.5
Ž . Ž
. Ž
. Ž
. 50 II
13.3 5.1 5.7 3.9
7.6 3.7 Ž .
Ž .
Ž .
Ž .
Day 21 0 I
60.9 26.1 35.6 19.2
25.4 9.2 89.7
Ž . Ž
. Ž
. Ž
. 0 II
75.1 35.7 43.6 23.9
31.5 16.2 Ž .
Ž .
Ž .
Ž .
50 I 5.6 4.9
4.3 3.4 1.3 2.0
Ž . Ž
. Ž
. Ž
. 50 II
8.3 3.8 3.0 1.8
5.3 3.2
3.4. Third trial 7.2–8.58C 3.4.1. Third trial: efficacy against L. salmonis
Table 5 shows the efficacy and mean numbers of L. salmonis for the third trial. Prior Ž
. to the start of treatment there were no significant P 0.05 differences in lice numbers
between pens.
Ž .
Fig. 1. a and b Third trial: Efficacy of emamectin benzoate against natural infestations of L. salmonis on Atlantic salmon. Fish received medicated feed at the rate of 0.5 biomass per day for 7 consecutive days.
Sample size N s 20 fish per pen. Between days 27 and 55, after the trial period, only five fish in control pen II and treated pen I were evaluated. Chalimus were counted only up to a maximum of 100 per fish. Sea
temperatures 7.2–8.58C from days y1 to 20 and 8.8–10.98C from days 22 to 55.
Over the trial period, L. salmonis numbers increased by 170 in the two control groups. There was no corresponding increase on treated fish and, from days y2 to 21,
lice numbers decreased by 68. At days 14 and 21, both treated groups had signifi- Ž
. cantly P - 0.01 fewer L. salmonis than the two control groups. At day 21, the two
treated groups still had a higher mean number of lice compared to the results in the two summer trials, although the mean numbers of lice on control fish were also much higher.
The number of L. salmonis on any individual control fish was 28–154 while the range on treated fish was only 0–19. At day 21, 20 of fish in the control groups had
characteristic lesions caused by sea lice while only 2.5 of treated fish were affected.
Ž .
At the end of the trial day 22 , all the pens on the site, with the exception of the two pens treated with emamectin benzoate, were subjected to a hydrogen peroxide bath
treatment for sea lice. The two pens treated with emamectin benzoate were not treated with hydrogen peroxide because of low lice numbers and improved appearance of the
fish. Following treatment with hydrogen peroxide there was a decline in the mean
Ž .
number of motile lice on control fish at day 27 Fig. 1a , but chalimus were not reduced Ž
. and increased to more than 100 per fish between days 35 and 55 Fig. 1b . As a result, at
day 55, mean motile lice numbers reached high levels again and a second hydrogen peroxide treatment had to be carried out 5 weeks after the previous treatment. After day
27, lice numbers on fish treated only with emamectin benzoate increased relatively slowly compared to the control group, and at day 55, treated fish still had 78 fewer
chalimus and 86 fewer motile lice than control fish. Between days 22 and 55, fish in the surrounding commercial pens also had much higher numbers of lice than fish in the
pens treated with emamectin benzoate. Prior to treatment, sea lice damage was recorded on only 0–5 of fish in each pen. At day 21, 20 of control fish had sea lice damage
compared to only 2.5 on fish in the two treated groups.
3.4.2. Third trial: efficacy against C. elongatus There were few C. elongatus present during this trial. Mean numbers at the start of
the trial were only 0.1–1.0 per fish and at day 21, the means were 0 and 0.8 per fish in the treated groups and 0 and 1.4 per fish in the control groups.
4. Discussion
